This invention is in the field of devices for the treatment of neurological disorders in human subjects, particularly those disorders that originate in the brain.
The current state of the art in treating neurological disorders such as epilepsy or Parkinson""s disease involves either drugs or the open-loop electrical stimulation of neurologic tissue. Drug therapy has been shown to have significant short and long term side effects and is often ineffective. In U.S. Pat. No. 3,850,161, Liss describes a continuous closed-loop feedback system which will always feedback part of the brain EEG signal to separate electrodes so that if a large EEG signal occurs it will be fed back in an attempt to cancel out the original signal. This system does not take advantage of recently developed digital signal processing and microcomputer technology by which feedback signals can be activated only when a neurological event occurs, nor does it provide a practical means to recognize and intervene during early stages in the evolution of a neurological event. In addition, the Liss device is not programmable and it does not provide a means to record EEG signals. Examples of a xe2x80x9cneurological eventxe2x80x9d are the occurrence of an epileptic seizure or the occurrence of a migraine headache. A xe2x80x9cneurological eventxe2x80x9d is defined herein as either the precursor of an event such as an epileptic seizure, or the epileptic seizure itself. Maurer and Sorenson in U.S. Pat. No. 4,019,518 describe a combined internal/external system for electrical stimulation of the body with biphasic pulses but do not describe any means of detecting neurological events. Fischell in U.S. Pat. No. 4,373,527 describes a programmable medication infusion system but does not anticipate its use in response to a detected neurological event.
More recently, a device has been approved for human use to stimulate the vagus nerve in a continuous fashion with the objective of decreasing the rate of epileptic seizures. Clinical reports on such devices indicate only a modest degree of success in that only 50% of the patients experience a greater than 20% reduction in the rate of epileptic seizures. Another device that has been recently introduced into clinical practice utilizes continuous stimulation of the thalamus for the treatment of involuntary motion disorders such as Parkinson""s syndrome.
Neither of these two open-loop devices described above is highly effective for the treatment of a neurological disorder such as epilepsy, and neither anticipates the use of decision making in order to optimize a response to turn off the neurological event nor the recording of EEG signals.
The automatic implantable cardiac defibrillator is an example of a decision making device having data recording capability that has been successfully used in a decision based closed-loop mode for the treatment of ventricular fibrillation. However, the requirements for detection and treatment of ventricular fibrillation are significantly simpler and certainly different from the requirements for a device to detect and treat an impending epileptic seizure. Specifically, an implantable cardiac defibrillator requires only a single signal, namely the heart""s ECG, in order to detect a fibrillation event. What is more, only a single pair of electrodes is required for detection of the fibrillation event and that same pair of electrodes can be used to provide an electrical stimulus for electrical defibrillation. A heart defibrillator electrode is adapted to be placed on or in close proximity to the heart and is not suitable for use as a brain electrode.
Coker and Fischell in U.S. Pat. No. 4,581,758 describe sophisticated signal processing techniques using the sum of squared signals from two microphones to identify the direction with respect to a person from whom human speech originates. Although the Coker and Fischell patent teaches several signal processing techniques which may be applied with others to detect neurological events, the Coker and Fischell method is aimed at identifying the location of the speech source, while one of the goals of the present invention is to utilize the known location of the source of EEG signals to help identify an abnormal EEG which signifies an impending neurological event.
The NeuroCybernetic Prosthesis System recently made available for the treatment of epileptic seizures, utilizes continuous open-loop stimulation of the vegas nerve. This device does not sense the onset of an epileptic seizure, and it utilizes wires that are placed in the neck. Because of the frequent motions of such wires, they will have a tendency to fracture. No existing system utilizes electrodes, electrical wires and a control module that are entirely contained within the patient""s scalp and essentially all contained within the patient""s cranium. Such systems would not have any repeated bending of connecting wires thereby improving long term reliability. Furthermore, the NeuroCybernetic Prosthesis System does not use a rechargeable battery, nor does it utilize a separate external device controlled by the patient to activate the implanted system at the start of a neurological event in order to decrease the severity or time duration of the neurological event.
The present invention is a multiple electrode, closed-loop system for the treatment of certain neurological disorders such as epilepsy, migraine headaches and Parkinson""s disease. A purpose of the present invention is to overcome the shortcomings of all prior art devices for the treatment of such disorders. Specifically, the present invention combines a multi-electrode array with sophisticated signal processing techniques to achieve reliable detection of the onset of a neurological event (such as an epileptic seizure or migraine headache) typically originating from a focus of limited spatial extent within the brain. It is well known that in certain patients, epileptic seizures consistently originate from a single location within the brain. However, the system described herein is also adaptable for the treatment of a neurological event that involves a major portion or possibly all of the brain tissue.
The present invention also provides means for generating an ensemble of coordinated electrical stimuli designed to terminate the neurological event immediately upon (or even prior to) its onset. Thus, the present invention is a responsive detection and stimulation system for the early recognition and prompt treatment of a neurological event.
The present invention envisions a multiplicity of brain electrodes placed either within the brain, on the surface of the brain itself, or on the dura mater that surrounds the brain. Some one, several, or all of these brain electrodes can be used for detection of an abnormal neurological event such as an epileptic seizure. A responsive stimulation signal can also be applied to any one, several, or all elements of such an electrode array. The responsive stimulation signals sent to each electrode may be identical or they may be programmed to differ in amplitude, frequency, waveform, phase and time duration. It is also envisioned that sensing electrodes may be entirely separate from the electrodes used for responsive stimulation.
The present invention envisions that a neurological event can be reliably detected in the presence of a normal EEG signal and in the presence of external noise by the use of modem and sophisticated signal processing techniques. Specifically, the electrical signal from an epileptic focus within a specific and limited spatial region within the brain can be reliably detected by combining the signals received at different electrodes that are placed at different distances from the epileptic focus. To improve signal-to-noise ratio, the signal received at a specified location which is at a specific distance from the epileptic focus could have a specific time delay to account for the propagation time it takes for the signal to reach that electrode. For example, if a first electrode is located directly over the site of the epileptic focus and a second electrode is located at a distance of several centimeters from the focus, then to combine these two signals together to optimize detection of a neurological event, the signal at the first (closest) electrode must have an added time delay to account for the time required for the signal to arrive at the position of the second electrode. Thus cross-correlation of EEG signals in the time domain is envisioned to be within the scope of the present invention.
It is also envisioned that appropriate selection (i.e., location) of electrode sites can be used to enhance the reliability for detection and termination of a neurological event. Thus, the present invention envisions enhancement of detection by the use of the spatial domain as it applies to the positioning of detection and treatment electrodes.
Finally, the present invention also envisions signal-to-noise enhancement for optimizing the a detection of neurological events by searching for signals in a particular frequency domain. For example, a low-pass filter that excludes signals above 5 Hz could be used to enhance the reliability for detection of a neurological event for certain patients. In addition, detection may be enhanced by first conditioning the EEG signals using programmable, multiple step, signal processing. The processing steps that are envisioned for this signal conditioning include signal summing, squaring, subtracting, amplifying, and filtering.
It is also envisioned that any combination of techniques for signal detection in the time, spatial or frequency domain could be used for providing a highly reliable system for the detection of a neurological event.
The present invention envisions four different modalities for stopping the progression of a neurological event such as an epileptic seizure once it has been detected. A preferred method is to provide a responsive stimulation electrical signal, a second method is to release medication in response to the detection of an event, a third method is to provide an electrical short circuit in the vicinity of the epileptic focus to prevent the occurrence of a full epileptic seizure and a fourth method is the application of a sensory input through normal sensory pathways. Such sensory input could be acoustic (sound input), visual (light input), or other sensory input such as mechanical vibration or electrical stimulation of the skin. Of course it is envisioned that any two or more of these modalities can be used in combination in order to preclude, prevent or decrease the severity of a neurological event such as an epileptic seizure, migraine headache, Parkinson""s disease tremor, etc.
A valuable attribute of the present invention is the ability to record the EEG signal from any one or all of the detection electrodes. Typically the EEG signal would be continuously recorded in a first-in first-out (FIFO) digital data recording system where the current data over-writes the oldest data as memory storage capacity is exceeded. In the event that a neurological event was detected, the device would save the preceding several minutes of data while continuing to record subsequent EEG data after the application of a response such as responsive stimulation, short circuiting of some electrode(s) or the delivery of a bolus of medication. It is conceived that the device would hold in memory the recording made for several minutes both before and after the neurological event. These data would then be read out by the patient""s physician on a regular basis; e.g., every three months or more frequently if the device did not promptly terminate some neurological event. It is also anticipated that the patient could use a patient""s initiating device to trigger the retention of several minutes of data recording of the EEG signal from a pre-selected group of electrodes.
It is also conceived that certain other data be recorded that can be helpful to the physician for treating the patient. These additional data would include: (1) the number of neurological events detected since the last memory readout and; (2) the number of responses triggered by the neurological events that were delivered to the patient. Furthermore, the system can be programmed so that when a neurological event is detected, the electrical signal from any one or more of the multiple steps in the signal conditioning can be stored in a digital memory. Additionally, telemetry would be provided to the physician that would indicate the serial number of the device that is implanted in the patient and the date and time that each neurological event or patient initiated recording occurred.
Another valuable attribute of the present invention is the capability to program the functions and parameters of the system to enhance the detection of a neurological event and to optimize the system responses for stopping a neurological event such as an epileptic seizure. Examples of programmable functions and parameters are: (1) the time delay introduced for a signal being received from a specific electrode; (2) the use or non-use of a specific electrode; (3) the frequency response characteristic of the channel assigned to process the signal received from a specific electrode; (4) whether or not a particular electrode is electrically shorted to another electrode or to the metal case of the device after a neurological event has been detected; (5) the amplitude, frequency, duration, phase and wave-form of the response signal delivered to a specific electrode; (6) the allocation of memory for storing EEG signals as received from one or more electrodes; (7) determination as to whether or not the data from a particular electrode will be stored in memory; (8) the amplitude, frequency and time duration of an acoustic, visual, or other sensory input applied to the patient in response to the detection of a neurological event, and (9) the specification of statistical data (histograms) to be recorded; for example, the number of epileptic seizures and/or the number of responsive stimulations delivered since the last memory readout by an attending physician. These are some but not all of the programmable functions and parameters that the system might utilize.
It should be understood that a telemetry signal would be transmitted from the implanted device. External receiving equipment typically located in the physician""s office, would process that signal and provide a paper print-out and a CRT display to indicate the state to which all the parameters of the implanted device have been programmed. For example, the display would indicate which electrodes are active, what algorithm is being used for detection, what specific bandwidth is being used with a specific electrode, etc.
It should be understood that, unlike implantable automatic heart defibrillators which generate a responsive signal only after ventricular fibrillation has occurred, it is a goal of the present invention to prevent full development of an epileptic seizure or migraine headache before the actual occurrence of such an unwanted neurological event. In this regard, the present invention is entirely different from any implantable medical device (such as an automatic heart defibrillator) that always allows the unwanted event to occur.
A specific capability of this system is to provide electrical stimulation to a specific portion of the brain as the means of stopping a neurological event. It is believed that the earliest possible detection of a seizure and treatment of aberrant electrical activity from an epileptic focus has the highest probability of aborting the occurrence of a full seizure. It is envisioned that either through specific placement of treatment electrodes or by adjusting the phase of signals applied to an array of electrodes, stimulation can be directed to the location(s) within the brain that offer the highest probability of stopping the seizure.
It is believed that there is minimal or no effect if a responsive stimulation is produced from an erroneously identified event, i.e., a false positive. On the other hand, failure to identify a real event is highly undesirable and could cause the patient to undergo a severe seizure. Therefore, the design concept of the current invention is to predispose the decision making algorithm to never miss a real event while allowing a false positive rate to be detected at up to 5 times the rate of actual events.
Telemetry data transmitted from the implanted device can be sent to a physician""s workstation in the physician""s office either with the patient in the physician""s office or remotely from the patient""s home by means of a modem. The physician""s workstation can also be used to specify all of the programmable parameters of the implanted system.
A novel aspect of a preferred embodiment of this invention is that the entire implantable portion of this system for treating neurological disorders lies under the patient""s scalp. Such placement will either have the device located between the scalp and the cranium or the within a hole in the cranium. Because of size constraints, the intracranial location is the preferred embodiment. This concept of this invention is to allow the patient to have an implantation of a comparatively large neurostimulator device that is completely cosmetically hidden. This is in contradistinction to any implantation of such a neurostimulator in the chest region outside of the rib cage. Even an implantation in the abdomen (which could be more cosmetically acceptable) would require wires to pass through the neck which both makes a detectable, elongated bulge in the skin of the neck and also causes these wires to be repeatably twisted which can result in their breakage. Wires leading from a control module cosmetically hidden in a hole in the cranium can be placed under the scalp or under the cranium where they will not be visible and they will not be twisted. This makes the implantation of the control module and wires all under the scalp both more cosmetically acceptable and less prone to breakage.
The implantation of the control module into the cranium can also be improved by the use of a fairing located outside the control module that provides a smooth contour for the control module under the patient""s scalp. Also a spacer shim for placement under the flange(s) of the control module can be used to adjust the height of the control module within hole in the cranium. The neurosurgeon would be provided with a set of spacers of variable thickness to be placed between a flange and the cranium for height adjustment of the control module. A resorbable disk which could contain an anti-biotic and/or anti-inflammatory substance could be placed at the bottom of the hole in the cranium between the dura mater and the control module to further protect the brain tissue and to help prevent infection and/or inflammation.
It is also envisioned that brain electrodes will be connected to wires that terminate in an electrical connector that is removably attachable to the control module. In that way, a control module can be replaced without removing either the implanted brain electrodes or the wires that connect to those electrodes.
To assist the neurosurgeon in accurately placing the control module within a hole made in the cranium, it is envisioned that a template will be provided that allows marking of the top of the cranium along the perimeter where bone is to be removed to make a hole into which the control module will be placed.
The implantable portion of the system includes; (1) electrodes that lie in close proximity to or actually within the brain; (2) a control module that contains a battery and all the electronics for sensing, recording and controlling brain activity, (3) electrically conducting wires that connect the control module to the electrodes, (4) a buzzer providing an acoustic signal or electrical xe2x80x9cticklexe2x80x9d indicating that a neurological event has been detected, and (5) an input-output wire coil (or antenna) used for communication of the implanted system with any and all external equipment. The battery that provides power for the system and an electronics module are both contained within a metal shell that lies under the patient""s scalp. The metal shell which contains the electronics module and the battery collectively form the control module.
All electrodes connect by means of electrically conducting wires to electrical terminals that are formed into the metal shell. The electronics module is electrically joined to the brain electrodes by means of the shell""s electrical terminals which are electrically joined to the wires that connect to the brain electrodes.
An important aspect of the preferred embodiment of this device is the fact that the shell containing the electronics module and the battery, i.e. the control module, is to be placed in the cranium of the skull at a place where a significant volume of bone is removed. By placing the entire system within the cranium, (as opposed to having some wires extending into or through the neck to a control module in the chest) the probability of wire breakage due to repeated wire bending is drastically reduced. However, the present invention also envisions the placement in the chest or abdomen of a control module if a large battery or a large volume electronics module dictates such a large size for the control module that it cannot be conveniently placed within the cranium. Such a thoracic or abdominal placement of a control module would require wires to be run through the neck.
The present invention also envisions the utilization of an intracranial system for the treatment of certain diseases without placing wires through the neck. Specifically, an alternative embodiment of the invention envisions the use of electrodes in or on the brain with an intracranial control module used in conjunction with a remote sensor/actuator device. For example, blood pressure could be sensed with a threshold of, let us say 150 mm Hg, and if that pressure was exceeded, a signal transmitted by electrical conduction through the body from the remote sensor/actuator device could be received at the control module and that would cause brain stimulation in such a way as to reduce the blood pressure. Conversely, if the brain detects pain and provides a signal detectable by the intracranial system, a signal could be sent by electrical conduction through the body to a remote sensor/actuator device which could provide electrical stimulation to locally stimulate a nerve to reduce the perception of that pain. Still another example is that if the precursor of an epileptic seizure is detected, a remote actuator could be used to electrically stimulate one or both vagus nerves so as to stop the epileptic seizure from occurring. Such a remote device could be located in the trunk of the patient""s body.
Another important aspect of this invention is that a comparatively simple surgical procedure can be used to place the control module just beneath the patient""s scalp. A similar simple procedure can be used to replace either the battery or both the battery and the electronics module.
Specifically, if the hair on the scalp is shaved off at a site directly over where the control module is implanted, an incision can then be made in the scalp through which incision a depleted battery can be removed and replaced with a new battery, or a more advanced electronics module can replace a less capable or failed electronics module. The incision can then be closed, and when the hair grows back, the entire implanted system would be cosmetically undetectable. A good cosmetic appearance is very important for the patient""s psychological well being.
The manner in which the control module, the electrodes and the interconnecting wires are placed beneath the scalp is important for the successful implantation of the entire implantable system. Specifically, the control module is optimally placed in either the left or right anterior quadrant of the cranium. Because the large sagital sinus vein runs along the anterior-posterior center line of the cranium, it is inadvisable to run epidural wires through that region, and furthermore, it would be inadvisable to place the control module directly over that major vein. Since movement of the jaw causes motions of the scalp relative to the cranium, it is advisable to run the connecting wires for electrodes that must be placed on the anterior portion of the brain in the epidural space as opposed to running them between the scalp and the cranium. Since the middle meningeal artery and its branches run within grooves interior to the posterior section of the cranium, it would be inadvisable to connect to posterior placed electrodes by utilization of connecting wires positioned in the epidural space beneath the posterior portion of the cranium. Therefore, the connecting wires for electrodes to be placed on a posterior portion of the brain""s surface are best located beneath the scalp, then through burr holes in the cranium where they connect to any electrodes placed in a posterior position on the surface of the dura mater. Conversely, most of the length of the connecting wires for electrodes located in the anterior portion of the brain would be placed in the epidural space. In no case should epidural wires be passed through the anterior-posterior centerline of the brain where the large sagital sinus vein is located.
An important operational aspect of the implanted system is the use of an input-output coil formed from many turns of fine wire that is placed between the scalp and the cranium generally along the anterior-posterior center line of the head. All communication between the external equipment and the implanted system can be accomplished by magnetic induction through the hair and scalp of the patient. Examples of these signals are the readout of telemetry from the implanted system, or the changing of some operational parameter of the implanted system by means of a command from some piece of external equipment. Furthermore, such an input-output coil can be used to recharge a rechargeable battery that can be located inside the control module. Since the input-output coil can be placed on a posterior portion of the cranium, relative motion of the scalp and cranium should not be a problem in that region.
By placing the input-output coil in an appropriate site just beneath the scalp, the patient can be provided with a cap to be worn on the head which cap includes a flexible coil that can communicate by magnetic induction using an alternating magnetic field with the implanted input-output coil. Such a cap could be placed on the patient in the doctor""s office when the doctor wishes to read out stored telemetry or program one or more new parameters into the implanted system. Furthermore, the cap could be used by the patient at home for remote connection to the physicians workstation over telephone lines using a pair of modems, or the cap could be used to recharge a rechargeable battery located in the control module of the implanted system.
Another important aspect of the system is a buzzer that can be implanted just behind the ear on the outer or inner surface of the cranium or actually within a burr hole within the cranium. If a neurological event is detected, the buzzer can provide an acoustic output that is detectable by the patient""s ear or the buzzer can provide an electrical xe2x80x9cticklexe2x80x9d signal. The buzzer can be used to indicate to the patient that a neurological event such as an epileptic seizure is about to occur so that an appropriate action can be taken. Among the appropriate actions that could be taken by the patient is the application of an acoustic, visual or sensory input that could by themselves be a means for stopping a neurological event such as an epileptic seizure. The acoustic input could be by means of a sound producing, hearing aid shaped device that can emit an appropriate tone as to pitch and volume directly into the ear. The visual device could be from a light emitting diode in eyeglasses or a small flashlight type of device that emits a particular type of light at some appropriate flashing rate. A sensory input could be provided by, for example, an externally mounted electrical stimulator placed on the wrist to stimulate the median nerve or by a mechanical vibrator applied to the patient""s skin.
When any such acoustic, visual or other sensory input is actuated, either automatically or manually in response to the detection of a neurological event, literally billions of neurons are recruited within the brain. The activation of these neurons can be an effective means for stopping an epileptic seizure.
An alternative embodiment of the present invention envisions the use of a control module located external to the patient""s body connected to electrodes either external or internal to the patient""s scalp. Such an externally located control module might be positioned behind the patient""s ear like a hearing aid.
Thus it is an object of this invention to provide appropriate stimulation of the human brain in response to a detected neurologic event in order to cause the cessation of that neurologic event. Another object of this invention is to provide increased reliability for neurological event detection by the use of cross-correlated signals from multiple electrodes with appropriate time delay(s) to increase the sensitivity and reliability for detection from a specific area of the brain.
Still another object of this invention is to exploit a spectral characteristic of the signals from multiple electrodes to optimize the detection of a neurological event.
Still another object of this invention is to predispose the decision-making algorithm to allow false positives to cause a responsive stimulation but to disallow missing an actual event.
Still another object of this invention is to have the response to a neurological event be an electrical stimulation that is focused on a specific area of the brain by variably delaying the stimulation signal sent from each of several stimulation electrodes placed at different locations placed in close proximity to the brain or within the brain.
Still another object of this invention is to have the specific area of the brain onto which the response is focused be the area from which the event signal was detected.
Still another object of this invention is to record (and ultimately recover for analysis) the EEG signal(s) from one or more electrodes before, during and after a neurological event.
Still another object of this invention is to provide programmability for all-important operating parameters of the device.
Still another object of this invention is to provide recording of the certain functions of the device such as how many neurological events were detected and how many times the device responded to such detections.
Still another object of this invention is to use medication delivery as the response to a neurological event, either alone or in conjunction with electrical stimulation.
Still another object of this invention is to utilize implanted electronic circuitry which is adaptable to changing EEG input signals so as to provide self-adaptation for the detection and/or treatment of a neurological event.
Still another object of this invention is to have a system of electrodes connected by wires to a control module, the entire system being placed under the scalp and being essentially contained within the cranium.
Still another object of this system is to have essentially no flexure of interconnecting wires so as to enhance system reliability.
Still another object of this invention is to be able to replace a depleted battery within the system""s control module by a comparatively simple and quick surgical procedure.
Still another object of this invention is to be able to replace an electronics module within the system""s control module by a comparatively simple and quick surgical procedure.
Still another object of this invention is to be able to recharge the battery in the control module.
Still another object of this invention is to provide an externally situated patient""s initiating device that can be used by the patient when he or she senses that a neurological event is about to occur in order to provide a response for causing the stopping of that neurological event or in order to initiate the recording of EEG signals from a pre-selected set of electrodes.
Still another object of this invention is to utilize a remotely located sensor/actuator device within the body to detect an abnormal physiological condition and send an electrical signal with or without wires to a control module within the cranium which then responds by an electrical signal delivered to the brain to treat the abnormal physiological condition.
Still another object of this invention is to utilize an intracranial system for sensing some abnormal physiological condition and then sending an electrical signal with or without wires to a remote sensor/actuator device that is remotely located within the body to carry out some treatment modality.
Still another object of this invention is to provide a buzzer which indicates to the patient that a neurological event has occurred.
Still another object of the invention is to provide an implantable neurostimulator system that is cosmetically hidden within the patient""s body.
Still another object of the invention is to have one or more flanges attached to the control module that can be fixed to the cranium by means of mechanical attachment devices such as staples or bone screws.
Still another object of the invention is to have a selection of spacer shims for placement under the flange(s) of the control module to adjust the height of the control module within a hole made in the cranium.
Still another object of the invention is to have a resorbable disk that can contain an anti-biotic and/or anti-inflammatory substance, the resorbable disk being adapted for placement between the bottom of the control module and the dura mater.
Still another object of the invention is to have a detachable electrical connector to join the control module to the electrical wires that connect to brain electrodes.
Still another object of the invention is to have a template to mark the outline of the control module on the cranium prior to the removal of cranial bone for insertion of the control module.
Still another object of the invention is to have a fairing placed around the control module to provide a smooth surface under the scalp.
Still another object of this invention is to provide acoustic, visual or other sensory inputs to the patient either automatically or manually following the detection of a neurological event so as to stop the neurological event.
These and other objects and advantages of this invention will become apparent to a person of ordinary skill in this art upon careful reading of the detailed description of this invention including the drawings as presented herein.